How good can Sam Bradford be for the Eagles in 2015?

Entering the third year of the Chip Kelly era, the Eagles are at something of a crossroads. Yes, the team has won 20 games over the last two years, and won the NFC East in Kelly’s first year. But that was then. In many ways, the highlights of Kelly’s first game as head coach, the Monday night thrashing in Washington, seem almost like they came from another team, replaced by All Pro players like DeMarco Murray, and some, like Evan Mathis, not replaced at all.

But all of those moves are secondary to the one that may well ultimately define Kelly’s tenure in Philadelphia. Yes, more than trading the franchise’s all-time leading rusher. And yes, more than wresting control of the front office.

It’s the quarterback, stupid.

During the offseason Kelly traded incumbent starting quarterback Nick Foles and a second-round pick to the Rams in exchange for Sam Bradford, a quarterback with some elite-level tools and the dreaded label of "bust". Now, Kelly and the Eagles will try to take the next step with a quarterback who hasn’t played a full season since 2012. If Kelly’s style of team building hadn’t been considered unorthodox before, it certainly is now.

Bradford was supposed to be the franchise quarterback to lead the Rams out of the mire of mediocrity. Instead, he finished his five-year tenure in St. Louis with a record of 18-30-1, a 58.6 completion percentage and two consecutive ACL injuries. Bradford is still rehabbing his latest knee injury with the hopes of returning to the practice field by the start of training camp. If he can, he’ll be placed into a system that many observers have called "quarterback-proof".

But even if he is able to play come preseason, no one seems quite sure what to expect. He’s a quarterback with a good-to-great arm and above-average accuracy, even if his stats don’t necessarily show it. But is he better than Foles or Mark Sanchez, who finished last season as the starter in Philadelphia? And is it too late, in his sixth pro season, to fulfill the potential that got him drafted first overall?

Bradford finished his time in St. Louis with 11,065 passing yards, 59 touchdowns and 38 interceptions. Since 2000, 16 quarterbacks – Bradford included – have posted similar (or superior) stats in their first four seasons. Of those, four are entering their fifth seasons in 2015. As for the remaining 11, their fifth seasons provide some insight into what the Eagles might expect to see out of Bradford in 2015.

(It’s important to note here that Bradford missed the entire 2014 season with an ACL injury, and thus his numbers are being compared against players entering their fifth seasons.)